Two types of cultured cells, human hepatoma cells (Hep G2) and cultured human fibroblasts have been previously well characterized as regards their insulin receptors. The Hep G2 cells have now been evaluated in several bioassays for insulin responsiveness: glucose uptake, glycogen synthase activation, thymidine incorporation into DNA, uridine incorporation into RNA and carbon dioxide production from acetate. Insulin receptors from both Hep G2 cells and human fibroblasts have been solubilized and receptor and/or artificial substrate phosphorylation measured. The status of insulin stimulated phosphorylation using fibroblasts from several insulin resistant patients is under investigation. The insulin receptor in Chinese hamster ovary (CHO) cells have been identified and partially characterized. Two mutant CHO cell lines have been used to examine the role of glycosylation in receptor function and in receptor processing. Receptor glycosylation may be involved in receptor binding and may influence receptor affinity. The insulin receptor biosynthesis and insertion into the plasma membrane appears to occur normally even in mutant cell lines with major defects in receptor glycosylation. Lectins have been used as probes to determine glycosylation status of the insulin receptor in CHO cells and their mutants.